Field of the Invention
The present invention relates to an image display apparatus and a control method therefor.
Description of the Related Art
Conventionally, as a technique concerning a liquid-crystal display apparatus, a technique for using a backlight including a plurality of light sources to control light emission brightness (light emission amounts) of the light sources according to a statistic of input image data has been proposed (Japanese Patent Application Laid-open No. 2008-090076). By performing such control, it is possible to improve contrast of a displayed image (an image displayed on a screen). Such control (control for partially changing the light emission brightness of the backlight) is called “local dimming control”.
In an image display apparatus, a technique for calibrating, using an optical sensor that measures light (a displayed image) from a screen, display brightness and a display color (brightness and a color of the screen or brightness or a color of the displayed image) has been proposed (Japanese Patent Application Laid-open No. 2013-068810).
In the calibration of the image display apparatus, usually, a measurement value of each of a plurality of images for calibration displayed on the screen in order (a measurement value of the optical sensor) is used. Therefore, when the calibration is performed while the local dimming control is performed, during the execution of the calibration, in some case, light emission brightness of light sources changes and the measurement value of the optical sensor changes. As a result, the calibration sometimes cannot be highly accurately executed.
Japanese Patent Application Laid-open No. 2013-068810 discloses a technique for highly accurately performing calibration while performing the local dimming control. Specifically, in the technique disclosed in Japanese Patent Application Laid-open No. 2013-068810, when the calibration is performed, a change in light emission brightness due to the local dimming control is suppressed in light sources provided around a measurement position of an optical sensor. Consequently, it is possible to suppress the light emission brightness of the light sources provided around the measurement position of the optical sensor from changing during the execution of the calibration. It is possible to suppress a measurement value of the optical sensor from changing during the execution of the calibration.
However, in the technique disclosed in Japanese Patent Application Laid-open No. 2013-068810, if a region where a change in the light emission brightness due to the local dimming control is suppressed is large, an effect of improvement of contrast by the local dimming control decreases and the quality of a displayed image is deteriorated.
Since lights from the light sources disuse, in the technique disclosed in Japanese Patent Application Laid-open No. 2013-068810, if a region where a change in the light emission brightness due to the local dimming control is suppressed is small, the measurement value of the optical sensor sometimes greatly changes because of a change in the light emission brightness of the light sources in other regions. As a result, the calibration sometimes cannot be highly accurately executed.
Note that, not only when the local dimming control is performed but also when light emission of a backlight is controlled on the basis of input image data, the problems explained above (the deterioration in the quality of the displayed image, the deterioration in the accuracy of the calibration, etc.) occur.